Ebola is the latest in a long list of infectious disease outbreaks that have plagued humankind. The worst become pandemics, sweeping across continents and killing as many as tens of millions of people.

How much higher this epidemic’s death toll might climb remains to be seen. In late September, the U.S. Centers for Disease Control and Prevention estimated that in a worst-case scenario, the total number of cases (not deaths) could reach 1.4 million by late January.

Plague of Justinian (541-542):This bubonic plague outbreak spread throughout the Byzantine Empire but centered on the Mediterranean region. It halted the reconquest of lands once part of the Roman Empire.

Cholera: Cholera pandemics started in India in the 1800s. The seventh outbreak (still ongoing) started in Indonesia in 1961 and spread across Asia, the Middle East, and Africa.

Flu: Influenza pandemics have flared up several times and likely will again, as flu viruses mutate into new strains.

Typhus epidemic of 1847:Massive numbers died in Ireland. Others, fleeing disease and the famine of 1846, died in “coffin ships” and upon arrival as immigrants to U.S. and Canadian ports.

Great Plague of London (1665-1666): The last in a long series of London bubonic plagues that started in 1499, this epidemic killed about 20 percent of Londoners. It started to subside in early 1666 and finally ended after the Great Fire of London later that year.